Adjustable mirror assembly

ABSTRACT

A mirror assembly suitable for use in reflecting a laser beam or any other light beam, in which the mirror can be positioned to rotate about a pair of orthogonal axes to the plane of the reflective surface of the mirror. The mirror is mounted on the front of a trunnion having spherical peripheral side surfaces which are journaled in the corresponding spherical bearing surfaces of a surrounding cap. The center of the sphere along which the spherical trunnion surfaces and the bearing surfaces lie is located at the intersection of the orthogonal axes at the reflecting surface of the mirror about which rotation of the mirror is desired. The spherical trunnion surfaces and the spherical bearing surfaces are urged together by means of a partially compressed wave spring acting between a shoulder on the trunnion and a capture ring secured to the front of the cap. The trunnion has a rearward extension within the cap which can be adjustably positioned rotationally about the center of the spherical surfaces by means of set screws extending through the cap and bearing against the sides of the extension of 90* from each other. The above-described unit is preferably secured together as an integral module, which in turn can be removably secured to a baseplate on a mirror corner support, with the mirror extending through an opening in the baseplate and corner support so as to be exposed to the laser beam. The front of the mirror is positioned forwardly of the remainder of the module so that it can readily be cleaned.

United States Patent Field [151 3,642,353 Feb. 15,1972

[54] ADJUSTABLE MIRROR ASSEMBLY [72] Inventor: Richard 11. Field,Broomall, Pa.

[73] Assignee: Lasermation, Inc., Philadelphia, Pa.

[22] Filed: Oct. 2, 1970 211 Appl. No.2 77,435

[52] US. CL ..350/310, 74/89.15, 74/471 XY, 248/179, 248/481, 350/6 [51]Int. Cl. ..G02b /18 [58] Field of Search ..350/6, 7, 285, 288, 310;74/471 XY, 89.15; 248/179, 181, 481, 483

466,976 3/ 1914 France ..350/296 Primary Examiner-David SchonbergAssistant ExaminerJohn W. Leonard Au0mey-Howson and Howson [57] ABSTRACTA mirror assembly suitable for use in reflecting a laser beam or anyother light beam, in which the mirror can be positioned to rotate abouta pair of orthogonal axes to the plane of the reflective surface of themirror. The mirror is mounted on the front of a trunnion havingspherical peripheral side surfaces which are joumaled in thecorresponding spherical bearing surfaces of a surrounding cap. Thecenter of the sphere along which the spherical trunnion surfaces and thebearing surfaces lie is located at the intersection of the orthogonalaxes at the reflecting surface of the mirror about which rotation of themirror is desired. The spherical trunnion surfaces and the sphericalbearing surfaces are urged together by means of a partially compressedwave spring acting between a shoulder on the trunnion and a capture ringsecured to the front of the cap. The trunnion has a rearward extensionwithin the cap which can be adjustably positioned rotationally about thecenter of the spherical surfaces by means of set screws extendingthrough the cap and bearing against the sides of the extension of 90from each other. The above-described unit is preferably secured togetheras an integral module, which in turn can be removably secured to abaseplate on a mirror corner support, with the mirror extending throughan opening in the baseplate and comer support so as to be exposed to thelaser beam. The front of the mirror is positioned forwardly of theremainder of the module so that it can readily be cleaned.

ADJUSTABLE MIRROR ASSEMBLY BACKGROUND OF THE INVENTION There are a largevariety of important applications in which it is desirable or necessaryto support a mirror reflective of electromagnetic energy in a mannersuch that the angle of the mirror can be accurately adjusted. While suchadjustable mirror arrangements have long been useful in experimental orcommercial optical equipment utilizing ordinary light, they also findincreasingly important use in the reflection of laser light. Such laserlight is often utilized in the form of a narrow, highly collimated beamtraveling from a source to a final target along a path which may includeone or more reflections from mirrors. As an example only, in themachining of materials by impinging a laser beam thereon, it is known toplace the workpiece upon a horizontal work table, to direct the beamalong an X-direction parallel to the workpiece, to reflect it along aY-direction at right angles to the X-direction and parallel to theworkpiece by means of a first mirror, and then to direct the beamdirectly downwardly upon the workpiece by means of a second mirror, bothmirrors providing rightangle reflection of the beam. The point at whichthe laser beam strikes the workpiece is in general critical, and willdepend upon the exact angles of the mirrors, hence the angular positionsof the mirrors must be very accurately adjusted.

In such laser-beam machining apparatus, the point of impingement of thebeam upon the workpiece during use may be changed by appropriatelymoving the mirrors along the X- and Y-directions and arresting them atthe positions which direct the beam to the desired point. In order tocause the beam to move quickly to different successive points on theworkpiece, it is often important to move the mirrors rapidly betweentheir corresponding positions, a process which inherently involvesrelatively high accelerations of the mirrors. in such cases it is alsovery important that the mirror support arrangements have high-mechanicalstability, so that the angles of the mirror will not change in responseto such accelerations or shocks.

it is also generally important that the mirror be enclosed in a lightand environment impervious enclosure; in the case of conventionaloptical systems, this is normally to prevent entrance of stray lightinto the system, while in the case of a laser it is customary to enclosethe beam as a safety measure, particularly in high-power laser systems.in both cases, it is desirable to exclude contaminating atmospheres fromthe mirror surface and adjusting mechanism. Also, in such cases it ishighly desirable to be able to make adjustments of the mirror angle fromthe exterior of the light enclosure, rather than having to disassemblethe system in order to get at the mirror for adjustment purposes.

Also generally important is a provision for cleaning the reflectivesurface of the mirror from time to time. This makes it desirable thatthe mirror mounting structure be in the nature of an integral modulewhich can be removed relatively easily from the light enclosure onoccasions when cleaning is required, and readily replaced. In thiscircumstance it is desirable that the mirror mounting arrangement besuch that upon replacement the mirror assumes the same position which ithad before its removal.

In connection with the cleaning operation, it is also desirable that thesurface of the mirror to be cleaned be freely and openly accessible. Forexample, one typical method of cleaning such a mirror consists ofwetting the mirror with a cleaning liquid such as acetone and drawing asheet of lens tissue across the mirror surface with a downward pull. Ifthe mirror surface to be cleaned is recessed within its mountingstructure, such an operation becomes quite difficult.

in many such systems it is also important that the axis or axes aboutwhich the mirror is rotated during adjustment lie in the plane of thereflective surface of the mirror at the point where the reflection oflight occursv Unless this is true, angular adjustment of the mirror willnot only change the angle of the reflected light but will also causetranslational motion of the impinged portion of the mirror surface, thuschanging the path length traversed by the light, and in some casesshifting the lateral position of the reflected beam. However, if the twomutually orthogonal axes about which the mirror is rotated lie in theplane of the reflecting surface of the mirror and have theirintersection at the point of impingement by the beam, then pure angularrotation occurs, without translational motion.

One type of mirror mounting arrangement which has been utilized in thepast supports the mirror by means of a pair of orthogonally arrangedgimbals to permit independent angular adjustment of the mirror about twocorresponding mutually orthogonal axes in the reflective surface of themirror. However, undesirable complications ensue when one attempts touse such a gimbal mount in a manner permitting adjustment of the mirrorangle from the exterior of an enclosure housing the mirror. Sucharrangements also tend to be relatively unstable mechanically,particularly in response to severe accelerations or shocks, and themirror is typically rather difficult to remove and replace in itsoriginal location; it is also typically recessed in a position wheresimple cleaning operations are difficult to perform.

Accordingly, it is an object of the invention to provide a new anduseful mirror assembly.

Another object is to provide such an assembly which enables accurateadjustment of the angular position of the mirror.

Another'object of the invention is to provide such a mirror supportassembly which enables adjustment of the angular position of the mirrorabout mutually orthogonal axes lying in the plane of the reflectivesurface of the mirror and intersecting at the point of impingement oflight thereon.

A further object is to provide such a mirror assembly which permits themirror to be readily mounted in, and demounted from, a position within alight enclosure and to be adjusted in angular position from the exteriorof the enclosure when the mirror is mounted therewithin.

It is also an object to provide such a mirror assembly which is ofhigh-mechanical stability, particularly in response to rapidaccelerations or shocks.

lt is also an object to provide such a mirror assembly which includes anintegral module structure with respect to which the mirror can beadjusted angularly, which module can be removed as a unit from the lightenclosure and, when so removed, exposes the reflective surface of themirror in an nonrecessed accessible position suitable for easy cleaningthereof.

SUMMARY OF THE INVENTION These and other objects of the invention areachieved by the provision of mirror means having a reflective surfaceand trunnion means positioned behind the mirror means to which themirror means is secured, the trunnion means having side surfaces whichlie along a spherical surface having its center in the plane of thereflective surface of the mirror means; also employed are bearing meanshaving spherical bearing surfaces parallel to, and in sliding engagementwith, the side surfaces of the trunnion means, and resilient meansurging together the trunnion means and the bearing means to maintain theside surfaces of the trunnion means in contact with the bearingsurfaces, together with means for rotating the trunnion means withrespect to the bearing means about said center as said side surfaces andsaid bearing surfaces slide over each other. Rotation of the trunnionmeans then causes the mirror to rotate angularly about the center of thespherical surface in the plane of the reflective surface of the mirror,as desired.

A light-impervious cap preferably encloses the trunnion and the sidesurfaces of the mirror means, as well as to aid in keeping the mirrorclean. In the preferred form the means for rotating the trunnion meanscomprises a rearward extension of the trunnion means, together withmeans for adjustably positioning the rearward extension rotationallywith respect to said center of said spherical surface, preferably bymeans of variably positionable means such as set screws extendingthrough the cap along two mutually orthogonal directions and bearingagainst the sides of the extension at points spaced by 90 around theextension. By adjustment of the set screws, the mirror can be tiltedadjustably about two mutually orthogonal axes in the plane of thereflective mirror surface.

The resilient means for urging together the side surfaces of thetrunnion means and the bearing surfaces is preferably a wave springpositioned between a capture ring secured to said cap and a shoulder onthe trunnion, all of the foregoing elements of the assembly preferablybeing secured together as an integral modular unit which can beremovably mounted upon a base plate on a corner support having anopening for receiving the mirror, so that when the module is mounted onthe corner support theopening is closed to light and the mirror frontsurface is exposed to the light beam to be reflected. Preferably thefront surface of the mirror is positioned forwardly of the remainder ofthe mirror module, so that the mirror can be easily cleaned when themodule is removed.

The assembly therefore provides for external control of the angularposition of a mirror within an enclosure, about two mutually orthogonalaxes lying in the plane of the reflective surface of the mirror, whicharrangement is highly stable mechanically, can easily be removed andreplaced, and provides for ready cleaning of the mirror when theassembly is removed from the corner support.

BRIEF DESCRIPTION OF FIGURES These and other objects and features of theinvention will become more readily understood from the consideration ofthe following detailed description, taken in connection with theaccompanying drawings, in which:

FIG. 1 is an elevational view, partly broken away, showing a mirrorassembly mounted on a corner support, and constructed in accordance withthe invention;

FIG. 2 is a plan view of the assembly of FIG. 1;

FIG. 1A is an exploded perspective view of the mirror assembly of FIG.1;

FIG. 3 is an enlarged sectional view taken along lines 33 of FIG. 2;

FIG. 4 is a sectional view taken along lines 4-4 of FIG. 1;

FIG. 5 is a sectional view taken along lines 5-5 of FIG. 3;

FIG. 6 is a fragmentary sectional view taken along lines 6- 6 of FIG. 5;

FIG. 7 is a fragmentary sectional view taken along lines 7 7 of FIG. 5;and

FIG. 8 is a perspective view of a wave spring utilized in the embodimentof the invention shown in the preceding figures.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Referring now by way ofexample only to the particular embodiment of the invention illustratedin the drawings, showing a mirror support assembly suitable for use inreflecting a laser or other light beam, the corner support 10 comprisesa pair of hollow tubular members 12, 14 having their axes disposed atright angles to each other and intersecting at a point P. The incidentbeam of electromagnetic radiation 16, this example assumed to be ahighly collimated laser beam, passes along the axis of tubular member12, and strikes the front surface of mirror 18 at the point P, whichsurface is at 45 to the incident beam thereby to produce a reflectedlaser beam 20 traveling at right angles to the incident beam and alongthe axis of the tubular member 14. Comer support 10 also comprises aboxlike corner chamber 22 on which the tubular members 12 and 14 aresupported in light-sealed fashion. The general shape of the cornerchamber 22 is that of a square box the rear portion of which has beencut off a plane at 45 to the laser beam, thereby to provide a rearopening bounded by peripheral mounting surfaces such as 26. A baseplate28 of rectangular form is secured to the latter mounting surfaces bymeans of screws such as 30. Baseplate 28 is provided with a largecircular opening 32 for receiving mirror 18, with appropriate ampleclearance.

The mirror 18 is supported on an integral minor support module 34 (seeespecially FIG. IA), which is readily mounted on and demounted from thebase plate 28 by means of the screws such as 38 which extend through aperipheral flange 40 on the surrounding module cap 42.

The mirror 18 may be of any well-known type utilized for laser beamreflection in which the reflective surface is the front surface of themirror. The mirror 18 is mounted on the flat front face of a mirrortrunnion 46, in this example by means of three spring clips 48 ofgenerally U-shape, each having one leg extending into a narrowperipheral slot 50 in the side of the mirror trunnion and the other legextending over the edge of the front surface of the mirror. The trunnion46 is preferably of a hard, heat-conductive material such as aluminum,and if desired a heat-transmissive viscuous layer of material may beapplied between the mirror and the trunnion to assure good heat transferfrom the mirror to the trunnion in applications where the laser beam issuch as to produce substantial heating of the mirror.

The module 34 includes a capture ring 54 having an inner forwardlyextending flange 56 which fits closely within the corresponding openingin the baseplate 28 so as to provide accurate seating of the module onthe baseplate. The capture ring is held to the cap 42 by means of screwssuch as 60, and

fits closely against a surrounding shoulder 62 of the cap. The trunnion46 is provided with a peripheral shoulder 64 facing toward the mirror,and a circular wave spring 66 (see especially FIG. 8) is positionedbetween the capture ring 54 and the trunnion shoulder 64, the springbeing of such configuration that when the screws 60 are tightened andthe trunnion is in the position shown, the spring is partiallycompressed, e.g., compressed by one-half of its range of compression.The trunnion 46 is provided with peripheral side surfaces 69 which liealong a spherical surface, the center of which is the point P at whichthe beam is reflected from the front of the mirror. In this example,these side surfaces comprise surfaces such as would be produced by thecutting of a sphere by a pair of parallel planes, and thus may bedescribed as the surfaces of a truncated sphere.

The cap 42 is provided with interior bearing surfaces 70 which havesubstantially the same form as that of the spherical side surfaces ofthe trunnion 46. Accordingly, the latter bearing surfaces are sphericalabout the point P, therefore being parallel to the trunnion sidesurfaces. By the action of the wave spring 66, the spherical trunnionside surfaces are biased against the bearing surfaces 70 in cap 42, andbecause of the spherical concentric nature of the bearing surfaces andthe trunnion side surfaces, the trunnion can be tilted angularly aboutthe point P, with a sliding motion of the trunnion side surfaces overthe adjacent bearing surfaces 70.

To facilitate such tilting of the mirror trunnion, the trunnion isprovided with a rearward extension 74, in the form of a rod of squarecross section in this example, and the cap 42 is provided with means forrotating the rearward extension 74 about the center P. In this example,these means constitute the four setscrews 76, 78, and 82 extendingthrough the walls of the cap 42, and having crowned ends which bearagainst the extension 74 at points spaced from each other by around theextension, as shown particularly clearly in FIG. 4. By backing off anyone of the setscrews and advancing the opposite setscrew, the desiredaccurate angular positioning of the mirror can be effected. Thelongitudinal axes of the adjusting screws are tangent to the continued(projected) trunnion spherical surface having its center at point P.Preferably the axes of one opposite pair of set screws 78, 82 lie in theplane of the incident and reflected beams 16, 20 and the axes of theother setscrews 76 and 80 lie in a plane at right angles to the lattertwo planes. With this arrangement of setscrews, independent adjustmentcan be provided about a pair of mutually orthogonal axes intersecting atpoint P and lying in the plane of the reflective surface of the mirror18.

It will be understood, however, that the particular means utilized tovary the angular position of the trunnion may depart substantially fromthe setscrew arrangement shown, and may comprise for example any of avariety of precision vernier positioning devices, manually orautomatically controlled, and may in some cases include apparatus forvarying the angle of the trunnion, and hence of the mirror, for thepurpose of providing slight scanning of the reflected beam duringoperatron.

Referring particularly now to H6. 1A, in assembling the device themodule 34 is first assembled, which may be accomplished as follows. Thesetscrews 76, 78, 80 and 82 are retracted just sufficiently toaccommodate the extension 74, the mirror 18 is clipped on to the frontof the trunnion 46 by means of the spring clips 48, the trunnion isdropped carefully into the cap 42 so that the extension 74 positionsitself generally as indicated in FIG. 4, the wave spring 66 ispositioned about the front of the trunnion, and the capture ring 54 isscrewed on to the front of the assembly to provide slight, but notexcessive, pressure between the spherical trunnion surfaces and thespherical bearing surfaces of the cap. The baseplate 28 is screwed intoposition over the rear opening of the corner chamber 22 of the cornersupport 10, and the module 34 positioned on the baseplate. To assureproper angular position of the module at this time, an indexing pin 90(see also FIG. 6) is preferably provided near the periphery of the cap42, the pin having a conical point extending forwardly so as to engagein the corresponding recess 92 in the base plate when the module is inits desired rotational position. Another setscrew 84 may be screwed intothe cap behind and against the index pin 90 to lock it into position.The screws 38 may then be tightened to hold the module in position onthe corner support. The setscrews 76, 78, 80 and 82 may then be adjusteduntil the desired alignment of the reflected laser beam is obtained.Where any subsequent readjustments are necessary, the module need not beremoved or disassembled, but the setscrews are merely adjusted from theexterior of the cap 42. When it is desired to clean the mirror, it isonly necessary to remove the module 34 by loosening the screws 38 andthen to clean the front surface of the mirror in any conventionalmanner, the latter surface extending forwardly of the remainder of themodule so as to facilitate such cleaning. The module may then bereplaced as described in connection with its initial installation,without upsetting the angular adjustment of the mirror.

Even with relatively coarse setscrews for adjusting the mirror angle,the apparatus shown can readily provide a 3 range of adjustment of themirror position, with a resolution of approximately 60 minutes of arcper revolution. The use of finer threads of the setscrews, or the use ofdifferential screw drives or other precision vemier arrangements, willprovide a considerably greater accuracy of adjustment.

It is also noted that the mirror trunnion is held against translationalmotion in one direction by the relatively firm wave spring 66, ispositively held against translational motion in all other directions bythe support provided by the spherical bearing surfaces 70 on theinterior of the cap 42, and is positively held in its angularly adjustedposition by the setscrews 76, 78, 80 and 82. Accordingly, the assemblyalso possesses a high degree of stability, particularly in the presenceof rapid accelerations or shocks.

Accordingly, while the invention has been described with particularreference to specific embodiments in the interest of completedefiniteness, it will be understood that it may be embodied in a widevariety of forms diverse from those specifically shown and described,without departing from the scope and spirit of the invention as definedby the appended claims.

What is claimed is:

l. A mirror assembly, comprising:

mirror means having a reflective surface;

trunnion means positioned behind said mirror means, and

means securing said mirror means to said trunnion means; said trunnionmeans having side surfaces which lie along a spherical surface havingits center in the plane of said reflective surface; bearing means havingspherical bearing surfaces parallel to,

and in sliding engagement with, said side surfaces of said trunnionmeans;

resilient means urging together said trunnion means and said bearingmeans to maintain said side surfaces in contact with said bearingsurfaces; and

means for rotating said trunnion means, with respect to said bearingmeans, about said center as said side surfaces and said bearing surfacesslide over each other, said means for rotating said trunnion meanscomprising a rearward extension of said trunnion means and means foradjustably positioning said rearward extension rotationally with respectto said center of said spherical surface.

2. The assembly of claim 1, comprising a cap extending over and aroundsaid rearward extension of said trunnion, and said means adjustablypositioning said rearward extension comprises variably positionablemeans extending through said cap and bearing against the sides of saidextension.

3. The assembly of claim 2, in which said variably positionable meanscomprise four elements bearing against the sides of said extension atpoints apart from each other about said extension.

4. A laser mirror-comer assembly, comprising:

a laser mirror having a plane reflective front surface;

a mirror trunnion, and means mounting said mirror on the front face ofsaid trunnion so that said front surface of said mirror is positionedforwardly of said trunnion;

said trunnion having circumferential side surfaces which are in the formof a segment of a sphere having its center at the center of said frontsurface of said mirror and having a rearwardly extending extension;

a trunnion cap enclosing the rear of said trunnion and said sidesurfaces thereof;

said trunnion cap having internal bearing surfaces of spherical formextending parallel to, and in sliding engagement with, said sidesurfaces;

a capture ring secured to said cap forwardly of said side surfaces;

a wave spring positioned between said ring and said cap;

a circumferential shoulder on said trunnion positioned partially tocompress said spring between said shoulder and said ring, thereby tourge said side surfaces against said bearing surfaces while permittingat least limited rotation of said trunnion with respect to said bearing;

adjustable screw means extending through said cap along two mutuallyperpendicular directions and bearing against said trunnion extension topermit adjustment of the rotational position of said trunnion and saidmirror by adjustment of said screw means;

said mirror, said trunnion, said cap, said ring and said spring, whensecured together, constituting an integral module;

a comer support comprising a pair of hollow tubular members the axes ofwhich intersect each other at said center of said mirror front surface,for passing the incident and reflected laser beam;

a baseplate mounted on said corner support at 45 to said axes andprovided with an opening for receiving said mirror when said module issecured to said baseplate; and

means for removably securing said module to said baseplate to close saidopening and expose said mirror front surface to said laser beam.

5. The assembly of claim 4, in which said screw means comprise fourscrews contacting said trunnion extension at points spaced from eachother by 90 about said extension.

1. A mirror assembly, comprising: mirror means having a reflectivesurface; trunnion means positioned behind said mirror means, and meanssecuring said mirror means to said trunnion means; said trunnion meanshaving side surfaces which lie along a spherical surface having itscenter in the plane of said reflective surface; bearing means havingspherical bearing surfaces parallel to, and in sliding engagement with,said side surfaces of said trunnion means; resilient means urgingtogether said trunnion means and said bearing means to maintain saidside surfaces in contact with said bearing surfaces; and means forrotating said trunnion means, with respect to said bearing means, aboutsaid center as said side surfaces and said bearing surfaces slide overeach other, said means for rotating said trunnion means comprising arearward extension of said trunnion means and means for adjustablypositioning said rearward extension rotationally with respect to saidcenter of said spherical surface.
 2. The assembly of claim 1, comprisinga cap extending over and around said rearward extension of saidtrunnion, and said means adjustably positioning said rearward extensioncomprises variably positionable means extending through said cap andbearing against the sides of said extension.
 3. The assembly of claim 2,in which said variably positionable means comprise four elements bearingagainst the sides of said extension at points 90* apart from each otherabout said extension.
 4. A laser mirror-corner assembly, comprising: alaser mirror having a plane reflective front surface; a mirror trunnion,and means mounting said mirror on the front face of said trunnion sothat said front surface of said mirror is positioned forwardly of saidtrunnion; said trunnion having circumferential side surfaces which arein the form of a segment of a sphere having its center at the center ofsaid front surface of said mirror and having a rearwardly extendingextension; a trunnion cap enclosing the rear of said trunnion and saidside surfaces thereof; said trunnion cap having internal bearingsurfaces of spherical form extending parallel to, and in slidingengagement with, said side surfaces; a capture ring secured to said capforwardly of said side surfaces; a wave spring positioned between saidring and said cap; a circumferential shoulder on said trunnionpositioned partially to compress said spring between said shoulder andsaid ring, thereby to urge said side surfaces against said bearingsurfaces while permitting at least limited rotation of said trunnionwith respect to said bearing; adjustable screw means extending throughsaid cap along two mutually perpendicular directions and bearing againstsaid trunnion extension to permit adjustment of the rotational positionof said trunnion and said mirror by adjustment of said screw means; saidmirror, said trunnion, said cap, said ring and said spring, when securedtogether, constituting an integral module; a corner support comprising apair of hollow tubular members the axes of which intersect each other atsaid center of said mirror front surface, for passing the incident andreflected laser beam; a baseplate mounted on said corner support at 45*to said axes and provided with an opening for receiving said mirror whensaid module is secured to said baseplate; and means for removablysecuring said module to said baseplate to close said opening and exposesaid mirror front surface to said laser beam.
 5. The assembly of claim4, in which said screw means comprise four screws contacting saidtrunnion extension at points spaced from each other by 90* about saidextension.